Abstrak. Pengukuran dengan menggunakan Ground Penetrating Radar (GPR) dilakukan di kawasan lumpur Sidoarjo tepatnya di daerah Tanggulangin, Sidoarjo, agar dapat memetakan bawah permukaan di daerah ini. Ground Penetrating Radar adalah metoda geofisika yang dikembangkan sebagai salah satu alat bantu untuk penelitian geologi bawah permukaan dangkal dengan menggunakan prinsip dari gelombang elektromagnetik dan memiliki hasil yang rinci. Penelitian ini dilakukan di utara pusat semburan lumpur dengan mengambil data sebanyak 8 lintasan, setelah itu data di olah menggunakan software MatGPR R3-5. Berdasarkan hasil pengolahan data diketahui bawah permukaan pada daerah penelitian sudah tidak stabil hal ini dikarenakan efek dari semburan Lumpur Sidoarjo. Kata Kunci-Ground Penetrating Radar (GPR), Lumpur Sidoarjo, Pemetaan bawah permukaan Abstract. Measurements with Ground Penetrating Radar (GPR) has been applied for subsurface imaging of Sidoarjo's Mud Volcano eruption in Tanggulangin, Sidoarjo. Ground Penetrating Radar is geophysical method which develop as one of devices for low subsurface geological research that use electromagnetic wave principle and it has very detailed result. This research is located in the north side of the mudflow center used data from 8 line, then the data was processed using MatGPR R3-5 software. Based on the processing result is known that subsurface in the measurement areas are unstable caused by the Sidoarjo's Mud Volcano Eruption.

Indonesia is the largest archipelagic country consisting of 17,504 islands which have 99,093 km of coastline. From the total, approximately only 10% had mapped. The coastline is essential for several applications such as topographic height reference, a reference in the delimitation of the marine management area, coastal boundaries, etc. Law number 4 of 2011 (UUIG), in article 13 paragraph 2 concerning Geospatial Information, mentioned three types of coastlines, namely: (a) the lowest astronomical tide, (b) the highest astronomical tide, and (c) the mean sea level. The existing method for determining the coastlines is observing a tide gauge over a long period at several places, then densify the point height by levelling method. This method is less effective due to time, cost, and amount of sample points. This paper presents our experience on coastlines determination by extracting it from a digital terrain model (DTM). The Airborne Topo-Bathymetric LiDAR technology is utilized to provide DTM that covers land and seabed. The points cloud, which is the output of this technology, was transformed to the geoid and corrected by tidal datum before those three types of coastlines were determined and delineated. The Western Part of Java Island is a study area. The project covers 1,000 km of coastline. The DTM quality was validated using several independent check-points along the coastline and hundreds of shorelines transect points at two locations. The result shows that vertical accuracy within the decimeter level.